Screw clearance holes

[Terry McClean]

I'm used to working in construction lumber.

I just tried to attach some 1.5 inch maple to a thick piece of white ash. I used my usual screw clearance bits but when I tried to drive the screws through the maple and into the ash, it was really tough and I finally snapped off the head. (Don't know when to stop!)

Any guidelines for what I should have done?

Thanks.

[Bobby Hatfield]

I'm used to working in construction lumber.

I just tried to attach some 1.5 inch maple to a thick piece of white ash. I used my usual screw clearance bits but when I tried to drive the screws through the maple and into the ash, it was really tough and I finally snapped off the head. (Don't know when to stop!)

Any guidelines for what I should have done?

Thanks.


Terry, what type screws and clearance was used ? If that was hard maple and without a large enough pilot hole in either, its no wonder the screw sheared, neither wood compresses to any extent. It also binds on the dry screw, making driving harder. I use clearance bits at least as large as the root diameter, screw size less threads, in the receiving piece and larger to maybe a 64th under the whole screw size in the fastened piece in hardwoods. If the screw will be left to show on the piece, I will countersink for the head unless it is a binding type head, then I counterbore for the head if it will be left to show. Also a lubricant on the screws will help, take time to go to McFeeleys.com screw company and order a free screw catalog, it has much info on all types of screw setting jobs and a great assortment of screws, drivers, tools and other handy things.

[Glenn Clabo]

Bobby is right on...but I'll add a little more info. This all depends on how thick the wood is...and what you're trying to do. But if you want to pull the two parts together you'll notice the shanks of wood screw are unthreaded, so clearance holes should be drilled in the top piece of wood, this will allow it to be pulled tight onto the underlying surface. Here's a table I use...

[Carl Eyman]

Bobby & Glen are both right on. but there is one more caution. If the thicknesses of the two pieces and the design of the screw is such that there will be thread in both pieces of wood, it will be difficult to pull the top piece tight to the bottom piece. Be sure the top piece has a clearance hole that won't engage the threads. Some screws have an un-threaded shank that is smaller in diameter than the threaded portion. but may not be as long as the thickness of the top piece. Just an extra $.02 worth.

[Terry McClean]

Thanks for the response.

I was using 2 inch #8 wood screws. It's now clear that my clearance holes were not big enough, but also with a 2 inch screw going through inch and a half maple, that threads were engaged in both the maple and the ash and that presented problems.

So, I'll drill bigger clearance holes, drill a deeper counter bore so no threads are engaged in the maple, and lubricate the screws.

Now if I can just figure out how to remove the snapped screw part from the maple.

[Charles McKinley]

Thanks for the response.

I was using 2 inch #8 wood screws. It's now clear that my clearance holes were not big enough, but also with a 2 inch screw going through inch and a half maple, that threads were engaged in both the maple and the ash and that presented problems.

So, I'll drill bigger clearance holes, drill a deeper counter bore so no threads are engaged in the maple, and lubricate the screws.

Now if I can just figure out how to remove the snapped screw part from the maple.

Try to get a roll pin just larger than the screw. File the left side of the seamup about 1/8". Chuck the other end in a reversable drill and slide it over the screw. The roll pin should grab the screw and turn it out. Got the tip from one of the magazines. Hope it works.

[Jason Roehl]

Here's a trick I've used without fail when the threads of a screw engage both pieces of wood. Drive the screw all the way in. At this point, there is likely a 1/16"-1/8" gap between the two pieces, depending on how tightly you could hold the pieces together. Now back the screw out until the pieces push back together (usually means the screw is all the way out of the second piece), then drive the screw back in. It's an extra two steps, but works in a pinch. I wouldn't do this if I had to drive alot of screws this way--I'd get the right screws with the proper length of lag.